Three maps overlain with analysis of the wave amplitude error metric on 2, 4, and 6 day forecasts.
250 hectopascal (hPa) analysis of the wave amplitude error (WAE) metric (color image) on day-2, day-4 and day-6 forecasts computed from the mean of four ensemble model members with the forecast initialized on 06/12 00 UTC. Larger values of WAE indicate increased departure from the analysis. Vectors show the wave activity flux error which is also computed from the mean of all four ensemble members. The dashed contours denote the analysis wind speed at 50 meters per second. The two black contours are the 10,400- and 10,700-meters geopotential height lines at 250 hPa. Panel (a–c) shows forecasts times day 6, 4, and 2 respectively. Panel c also includes a zoom-in over the North American domain showing the ensemble standard deviation in WAE computed from all four ensemble forecasting models, where the errors originate from a mesoscale convective system. Credit: Lojko et al. [2022], Figure 4 (modified)
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Atmospheres

Mesoscale thunderstorms over North America have been observed to sometimes precede poor weather forecasts over Europe. Lojko et al. [2022] use a case study to illustrate how errors in a mesoscale system can amplify errors in larger-scale synoptic waves downstream. They show that air motion with a signature of intense clockwise circulation at the top of severe thunderstorms can rapidly expand into synoptic scales (about 1,000 kilometers). This can cause forecast error in the jet stream and significantly modify its downwind evolution over the Atlantic. This study provides a bridge between global models that are starting to move into resolutions with convective systems partially resolved and the mesoscale models that resolve mesoscale convective systems to improve numerical weather prediction.

Citation: Lojko, A., Payne, A., & Jablonowski, C. (2022). The remote role of North-American mesoscale convective systems on the forecast of a Rossby wave packet: A multi-model ensemble case-study. Journal of Geophysical Research: Atmospheres, 127, e2022JD037171.

—Minghua Zhang, outgoing Editor in Chief, JGR: Atmospheres

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